The green AC load line indicates that the plate voltage swings from 75V The effective 1.64kΩ bias resistor creates a DC grid bias of -1.2V. This puts a total of 95kΩ + 78kΩ = 173kΩ plus the bias Triodes, so for the purposes of determining the DC operating point, theĮquivalent circuit for one triode doubles the resistor valuesįor the plate load resistor, let's use an average value of 95kΩ. The resistors connecting the cathodes to ground carry the current of two There is no feedback from the output transformer. The long tailed pair phase inverter uses a dual 100kΩ potentiometer design your amp using a structured, professional methodology. 2įundamentals of Guitar Amplifier System Design This represents power amp input sensitivity. The load line crosses it at a plate voltage of about 50VĪnd a plate current of about 135mA, so output power is in the neighborhood ofĪt full power, the signal at the grids is 10.2V peak, which is They act as references for an imagined curve for a 315V screen. The red load line therefore connects 322V, 0mA and 0V, 161mA. If the plate voltage swings from 322V down to 0V, the plate We divide the 8kΩ plate-to-plate primary impedance by 4 If we approximate audio performance by assuming pure Class B operation, The blue curve is for a 250V screen and 0V grid. The screen voltage is only slightly above 300V, so we can use 300V plate characteristics. master the basics of preamp, power amp, and power supply design. Guitar Amplifier Electronics: Basic Theory a cathode current (screen current plus plate current) of 34mA.a plate-to-cathode voltage of 322V, and.This is born out by the corresponding orange dot placed slightly above the dashed screenĬurrent curve, which indicates the screen current is 2.5mA.īased on this analysis, our estimate of the DC operating point for an average set of tubes is If the ratio of screen current to plate current is The DC plate current is 32mA for one tube. Plate current curve for a 300V screen (green dot), indicating The intersection of the blue and green lines is slightly above the These are the endpoints of the green line segments. If the grid bias is -10V or -11V, then the screen voltage is 315V or 314V, If the DC grid bias is -9V, then the cathode is at 9V and the If there is no plate current the voltageĪcross the cathode resistor is 0V, so the other endpoint represents If the plate current is 40mA, then according to Ohm's Law theĪ grid voltage of -12.8V and a plate current of 40mA is one endpoint Two tubes, so its equivalent value for one tube is double: 300Ω. The 150Ω cathode resistor carries the plate and screen current for New! Guitar Amplifier Electronics: Fender Deluxe - from TV front to narrow panel to brownface to blackface Reverb The ratio of cathode current to plate current is also constant: To screen current is approximately constant, Using the upper solid curve for plate current and the upper dashed curve for screen current, we see that for a -6.6V grid, the plate current is 65mA and the screen current is 5mA, as depicted by where the red line crosses the two curves. The power amp has a pair of EL84 pentodes in push-pull with cathode bias and no negative feedback.Ī Sovtek EL84 data sheet includes plate and screen transfer characteristics when both the plate and screen are at 300V. Both became near overnight successes and won awards from guitar magazines on both sides of the Atlantic." 1 -Dave Hunter Renditions using EL84-based output stages and manufactured with quality PCBs and a '99 respectively, captured great Orange-meets-Vox tones in thirty and fifteen-watt "Two of the new designs of a revitalized Orange, the AD30 and AD15 of 1998 and
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